QPoint Class

The QPoint class defines a point in the plane using integer precision. More...

Header:	#include <QPoint>
CMake:	find_package(Qt6 COMPONENTS Core REQUIRED) target_link_libraries(mytarget PRIVATE Qt6::Core)
qmake:	QT += core

• List of all members, including inherited members

Note: All functions in this class are reentrant.

Public Functions

	QPoint(int xpos, int ypos)
	QPoint()
bool	isNull() const
int	manhattanLength() const
int &	rx()
int &	ry()
void	setX(int x)
void	setY(int y)
CGPoint	toCGPoint() const
QPoint	transposed() const
int	x() const
int	y() const
QPoint &	operator*=(float factor)
QPoint &	operator*=(double factor)
QPoint &	operator*=(int factor)
QPoint &	operator+=(const QPoint &point)
QPoint &	operator-=(const QPoint &point)
QPoint &	operator/=(qreal divisor)

Static Public Members

int	dotProduct(const QPoint &p1, const QPoint &p2)

Related Non-Members

bool	operator!=(const QPoint &p1, const QPoint &p2)
QPoint	operator*(const QPoint &point, float factor)
QPoint	operator*(const QPoint &point, double factor)
QPoint	operator*(const QPoint &point, int factor)
QPoint	operator*(float factor, const QPoint &point)
QPoint	operator*(double factor, const QPoint &point)
QPoint	operator*(int factor, const QPoint &point)
QPoint	operator+(const QPoint &p1, const QPoint &p2)
QPoint	operator+(const QPoint &point)
QPoint	operator-(const QPoint &p1, const QPoint &p2)
QPoint	operator-(const QPoint &point)
QPoint	operator/(const QPoint &point, qreal divisor)
QDataStream &	operator<<(QDataStream &stream, const QPoint &point)
bool	operator==(const QPoint &p1, const QPoint &p2)
QDataStream &	operator>>(QDataStream &stream, QPoint &point)

Detailed Description

A point is specified by a x coordinate and an y coordinate which can be accessed using the x() and y() functions. The isNull() function returns true if both x and y are set to 0. The coordinates can be set (or altered) using the setX() and setY() functions, or alternatively the rx() and ry() functions which return references to the coordinates (allowing direct manipulation).

Given a point p, the following statements are all equivalent:

QPoint p;

p.setX(p.x() + 1);
p += QPoint(1, 0);
p.rx()++;

A QPoint object can also be used as a vector: Addition and subtraction are defined as for vectors (each component is added separately). A QPoint object can also be divided or multiplied by an int or a qreal.

In addition, the QPoint class provides the manhattanLength() function which gives an inexpensive approximation of the length of the QPoint object interpreted as a vector. Finally, QPoint objects can be streamed as well as compared.

See also QPointF and QPolygon.

Member Function Documentation

QPoint::QPoint(int xpos, int ypos)

Constructs a point with the given coordinates (xpos, ypos).

See also setX() and setY().

QPoint::QPoint()

Constructs a null point, i.e. with coordinates (0, 0)

See also isNull().

[static, since 5.1] int QPoint::dotProduct(const QPoint &p1, const QPoint &p2)

QPoint p( 3, 7);
QPoint q(-1, 4);
int lengthSquared = QPoint::dotProduct(p, q);   // lengthSquared becomes 25

Returns the dot product of p1 and p2.

This function was introduced in Qt 5.1.

bool QPoint::isNull() const

Returns true if both the x and y coordinates are set to 0, otherwise returns false.

int QPoint::manhattanLength() const

Returns the sum of the absolute values of x() and y(), traditionally known as the "Manhattan length" of the vector from the origin to the point. For example:

QPoint oldPosition;

MyWidget::mouseMoveEvent(QMouseEvent *event)
{
    QPoint point = event->pos() - oldPosition;
    if (point.manhattanLength() > 3)
        // the mouse has moved more than 3 pixels since the oldPosition
}

This is a useful, and quick to calculate, approximation to the true length:

double trueLength = std::sqrt(std::pow(x(), 2) + std::pow(y(), 2));

The tradition of "Manhattan length" arises because such distances apply to travelers who can only travel on a rectangular grid, like the streets of Manhattan.

int &QPoint::rx()

Returns a reference to the x coordinate of this point.

Using a reference makes it possible to directly manipulate x. For example:

QPoint p(1, 2);
p.rx()--;   // p becomes (0, 2)

See also x() and setX().

int &QPoint::ry()

Returns a reference to the y coordinate of this point.

Using a reference makes it possible to directly manipulate y. For example:

QPoint p(1, 2);
p.ry()++;   // p becomes (1, 3)

See also y() and setY().

void QPoint::setX(int x)

Sets the x coordinate of this point to the given x coordinate.

See also x() and setY().

void QPoint::setY(int y)

Sets the y coordinate of this point to the given y coordinate.

See also y() and setX().

[since 5.8] CGPoint QPoint::toCGPoint() const

Creates a CGPoint from a QPoint.

This function was introduced in Qt 5.8.

See also QPointF::fromCGPoint().

[since 5.14] QPoint QPoint::transposed() const

Returns a point with x and y coordinates exchanged:

QPoint{1, 2}.transposed() // {2, 1}

This function was introduced in Qt 5.14.

See also x(), y(), setX(), and setY().

int QPoint::x() const

Returns the x coordinate of this point.

See also setX() and rx().

int QPoint::y() const

Returns the y coordinate of this point.

See also setY() and ry().

QPoint &QPoint::operator*=(float factor)

Multiplies this point's coordinates by the given factor, and returns a reference to this point.

Note that the result is rounded to the nearest integer as points are held as integers. Use QPointF for floating point accuracy.

See also operator/=().

QPoint &QPoint::operator*=(double factor)

Multiplies this point's coordinates by the given factor, and returns a reference to this point. For example:

QPoint p(-1, 4);
p *= 2.5;    // p becomes (-3, 10)

Note that the result is rounded to the nearest integer as points are held as integers. Use QPointF for floating point accuracy.

See also operator/=().

QPoint &QPoint::operator*=(int factor)

Multiplies this point's coordinates by the given factor, and returns a reference to this point.

See also operator/=().

QPoint &QPoint::operator+=(const QPoint &point)

Adds the given point to this point and returns a reference to this point. For example:

QPoint p( 3, 7);
QPoint q(-1, 4);
p += q;    // p becomes (2, 11)

See also operator-=().

QPoint &QPoint::operator-=(const QPoint &point)

Subtracts the given point from this point and returns a reference to this point. For example:

QPoint p( 3, 7);
QPoint q(-1, 4);
p -= q;    // p becomes (4, 3)

See also operator+=().

QPoint &QPoint::operator/=(qreal divisor)

This is an overloaded function.

Divides both x and y by the given divisor, and returns a reference to this point. For example:

QPoint p(-3, 10);
p /= 2.5;           // p becomes (-1, 4)

Note that the result is rounded to the nearest integer as points are held as integers. Use QPointF for floating point accuracy.

See also operator*=().